Five among literati restored unknown theory (10)
I believe the answer is:
relativity
'theory' is the definition.
(I know that relativity is a type of scientific theory)
'five among literati restored unknown' is the wordplay.
'five' becomes 'V' (Roman numeral).
'among' is a charade indicator (letters next to each other).
'restored' indicates an anagram.
'unknown' becomes 'y' (algebra).
'v'+'literati'='vliterati'
'vliterati' is an anagram of 'relativit'.
'relativit'+'y'='RELATIVITY'
(Another definition for relativity that I've seen is " scientific principle".)